CRANIAL NERVES OF CAECILIANS 503 



THE OPTIC AND EYE-MUSCLE NERVES 



The rudimentary, or even vestigial, condition of the eyes in 

 the caeciUans is accompanied by a corresponding degeneracy of 

 the muscles of the eyeball and related nerves, with certain ex- 

 ceptions. Two degrees of degeneration occur. In one, as in 

 Dennophis, Geotrypetes, and Ichthyophis, the eye is covered by 

 the skin; in the other, as in Herpele and Caecilia, the eye is situ- 

 ated beneath the maxilla. In Dennophis, Ichthyophis, and 

 Geotrypetes the optic nerve, though rudmientary, may be traced 

 from the eyeball through the mass of the tentacular, or orbital, 

 gland, along the retractor muscle of the tentacle, thence through 

 the membranous wall of the cranial cavity and to its entrance 

 into the brain (figs. 14, 15, 17 to 19^^-^)- In Herpele and Cae- 

 cilia the eyeball is vestigial (fig. 10, oc.) and no trace of an optic 

 nerve is found. 



Of the eye-muscles and eye-muscle nerves in the caecilians vari- 

 ous accounts have been given. Wiedershemi does not mention 

 them. Waldschmidt describes an oculomotorius in Siphonops, 

 which anastomoses with the ramus maxillaris V and supplies 

 the compressor muscle of the orbital gland. Waldschmidt's 

 oculomotorius is probably a branch of the ramus mandibularis 

 V (7nd. 1 ) as will be shown later. He finds no trace of trochlearis 

 or abducens. Burckhardt agrees with Waldschmidt as to the 

 arrangement and innervation of the oculomotorius in Ichthyo- 

 phis. He finds no other eye-muscle nerves. The Sarasins found 

 in the embryo and adult of Ichthyophis four rectus and two 

 oblique muscles, besides a large retractor tentaculi which they 

 regarded as a modified retractor bulbi muscle. Of the innerva- 

 tion of these muscles they are uncertain. Leydig described four 

 muscles of the eyeball in Siphonops. Marcus finds in the em- 

 bryo of Hypogeophis all three eye-muscle nerves present, with 

 their characteristic distribution. The fourth nerve is extremely 

 attenuated; the sixth supplies the retractor tentaculi muscle, 

 and the oculomotorius a levator bulbi muscle. 



The writer finds in Dennophis four well-defined muscles at- 

 tached to the eyeball, in two sets. An anterior pair has origin 



